1. Field
The following description relates to optical communication, and more particularly, to an apparatus for transmitting/receiving variable-wavelength signals in a passive optical network.
2. Description of the Related Art
Fiber to the home (FTTH) based on wavelength division multiplexing (WDM), that is, a wavelength division multiplexing-passive optical network (WDM-PON), is a communication scheme in which communication between a central base station and subscribers is achieved using wavelengths respectively set for the subscribers. Such a communication scheme provides each subscriber with independent and highly secure, high-capacity communication service. In addition, the WDM based communication scheme, which is distinguished from a time division multiplexing (TDM) scheme, performs light source modulation/demodulation only for a subscriber, so even if the number of subscribers increases, the bandwidth provided to the subscriber does not change.
In order to implement the above WDM-PON, a light source having a number of unique wavelengths corresponding to the number of subscribers are needed. Accordingly, the use of a broadband variable-wavelength light source for colorless characteristics is one key to resolving an inventory issue (a difficulty in managing the inventory of light sources when fixed wavelength light sources are used and a n-channel providing system requires a total of n light sources).
That is, in order to implement the WDM-PON, there is a need for certain light sources having different wavelengths, which are allocated to fibers installed at each subscriber premises. Accordingly, when an ONT accesses a network, a series of initializing (allocation) functions, including an upstream light source wavelength allocation function and an arrangement function according to the allocated wavelength, are important.
A general wavelength initialization method uses an additional arrayed waveguide grating (AWG), an FP-filter, and a monitoring photo diode (PD). Such a conventional wavelength initialization method causes an increase in the cost of light sources and leads to a bulky structure, due to the additional cost of optical elements and the space taken by the optical elements. In order to compensate for such shortcomings, a wavelength initialization method using an optical layer has been suggested. According to this method, the wavelength is determined at an optical layer, based on an optical signal transmitted from an optical line terminal (OLT). A representative example of the wavelength allocation and wavelength initialization method above includes a wavelength initialization method using an external lookup table and a variable-wavelength optical transceiver using the same, disclosed in Korean Patent Publication No. 10-2008-0052332.
According to the conventional wavelength initialization method using an external lookup table and the variable-wavelength optical transceiver using the same, a wavelength initialization is performed by mounting a lookup table on a controller of an external host and sharing a control function including a lookup function with the host. The conventional wavelength initialization method using the external lookup table and the variable-wavelength optical transceiver using the same have a disadvantage in that when light sources are manufactured, the lookup table needs to be experimentally constructed and stored for a corresponding light source, and thus the number of light sources produced per unit time decreases.
In addition, optical signals use protocols, which leads to the paradox of wavelength initialization being impossible unless an initial optical path is set. That is, in the WDM-scheme where wavelength initialization represents setting of the optical path, in order to perform wavelength initialization using protocols, wavelength initialization needs to have already happened. The conventional TDM scheme, which uses a fixed wavelength, solves this paradox on the basis that the available wavelengths are fixed in the TDM scheme, so that wavelength initialization itself is not required.
In addition, the conventional wavelength initialization method using the external lookup table and the variable-wavelength optical transceiver using the same perform wavelength initialization through communicating with the OLT, and thus an error rate increases. In addition, the conventional wavelength initialization method using the external lookup table and the variable-wavelength optical transceiver using the same set the wavelength by use of a lookup table that is already set, and thus wavelength fine tuning is not achieved when each wavelength is set.